[By 1848], passenger traffic on the infant line being provided for, orders were given to supply some engines for the goods department. Accordingly, two classes of four-coupled engines were soon put to work, the one set Fig- 3- having four wheels only, all coupled, while the others ran on six wheels, the leading and driving wheels being coupled.
Of the former, six were built by Messrs. Bury, Curtis and Kennedy, and were all at work in 1848, receiving the railway Company’s Nos. 121 to 126, and, as can be seen from the accompanying illustration of No. 121, Fig. 3, were of the well-known “Bury” type of the period, having inside cylinders measuring 15-in. by 24-in., four-coupled wheels 5-ft. in diameter, the bar-frame, which was an integral factor of the type, and the modified circular, dome-topped firebox casing. Six other engines of almost the same pattern, numbered from Nos. 127 to 132, were built in 1848 and 1849 by Messrs. William Fairbairn & Sons, of Manchester, probably under contract with Messrs. Bury, who frequently sub-let part of their orders.
The accompanying drawing of No. 127, Fig. 4, with its tender, shows the main features of these engines, which had 15-in. by 24-in. cylinders, and 3-ft. 1-in. coupled wheels standing on a wheel-base of 7-ft. 8-in. The tender had four 3-ft. wheels on a 7-ft. 5-in. wheel-base, the total wheel-base of engine and tender being 27-ft. 11-in., with a length over buffers of 39-ft. 5-ins.
As can readily be understood, these twelve engines did not distinguish themselves to any praiseworthy degree by their capability for dealing with main-line traffic, which on this particular line, at all events, was of a heavier character than they were competent to work. Mr. Sturrock, therefore, afterwards converted them into six-wheeled, front-coupled engines, by the simple process of extending the framing rearwards, and adding a pair of 3-ft. trailing wheels under the footplate.
At the same time, he further dispensed with the tenders, providing Nos. 121 to 126 with saddle tanks carried over the barrel of the boiler, in the manner shown in the accompanying illustration, Fig. 5, and by this addition giving them a total weight of 29 tons 6 cwt., while Nos. 127 to 132 had side tanks.